I have a weird LaTeX error here. It seems as if the newline (\\) command is the culprit of a compilation error. The error shows up at the ending line of the .tex document: the \end{document} line, stating that this line has the undefined control sequence.

This code, though, is actually what causes the error.
This will compile (formatted incorrectly):

\defn{Method of Moments Estimator (MOME)}{a}
Properties of MOME:

But this won't compile (formatted correctly):

\defn{Method of Moments Estimator (MOME)}{a} \\
Properties of MOME:

The only difference is the \\ at the end of the line. I have no idea why this should not work.
For reference, this is the \defn command that I made:

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